CHAPTER XXVI 



GRASSLAND ASSOCIATIONS 



1. Natural Pasture. 



On the more gentle slopes of hills and mountains the 

 drainage is good, and the soil consequently dry. If an 

 abundance of plant-food is available in the soU, grasses 

 become established, and produce areas of natural pasture. 

 Grassland of this kind is found at all altitudes from sea- 

 level almost to the summits of the highest mountains, 

 more especially where the rocks are igneous or calcareous. 

 Sandstone hills rarely support a natural pasture, for 

 plant-food is scarce, and the slopes become covered with 

 grass-heath or calluna-heath (pp. 250, 252). 



The vegetation has to rely for its water-supply almost 

 entirely on atmospheric precipitations — -rain or dew. 

 Periods of drought are therefore frequent, whilst strong 

 drying winds prevail for a large part of the year. These 

 factors tend to favour the development of a xerophytic 

 type of vegetation, which becomes more pronounced at 

 high altitudes. 'The natural pasture forms the great 

 sheep-runs of all hilly districts, and the continual grazing 

 has a certain influence on the vegetation, many of 

 the taller plants being cut down to a few inches, and 

 prevented from producing flowers and seed. 



The turf is usually dense and compact, formed of the 

 fibrous shallow roots of the grasses, which monopolize 

 the water and food in the upper layers of the soil. The 

 only herbs which can obtain a footing are perennial 

 plants, whose long roots can explore the soil beneath 

 the turf, or hemi-parasites (p. 126), which become fixed 

 to the roots of the grasses and absorb much of their food 

 from them — e.g., Euphrasia officinalis (eyebright) and 



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